Television system



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Patented Mar. 30, 1943 UNITED STATES PATENT OFFICE TELEVISION SYSTEM Dudley E. Foster, South Orange, N. J., assigner to Radio Corporation of America, a corporation of Delaware Application september 2s, 1940,l serial Nb. 358,745

4 Claims. (Cl. 178-' l.5)

'I'he Vertical synchronizing pulses are then separated from the horizontal synchronizing pulses and each of. the signals is-then transmitted to their corresponding saw-tooth wave generators to produce the necessary deflection currents .in

the picture reproducing equipment. The synchronizing pulses are preferably in the black" picture direction and of greater amplitude in that direction than the blackest of the picture signals. A composite signal such as one including both picture signal and synchronizing pulses is illustrated in Electronics for July 1938 on pages 28 and 29. v

A number of systems have been proposed for clipping the synchronizing pulses from a composite signal by applying the composite signal to a discharge device having cathode and anode and a control electrode whereby the negative bias impressed upon the control electrode is of suflicient magnitude to aliow.the discharge device to pass only the synchronizing pulses.

It has also been proposed to provide a discharge device having a cathode and an anode and biased such that only the greater amplitude signals are passed therethrough.

According to this invention a discharge device having cathode, a controlelectrode and an anode together with an auxiliary diode anode adjacent the cathode is provided so that not only areA the synchronizing pulses clipped'from the composite video signal but the circuit may be adjusted to clip a predetermined portion in the range of amplitude occupied by the synchroniz- The cathode of the discharge device cathode win be negative with respect to the diode anode only as a result of the synchronizing pulses.

Accordingly'the principal object of this inven- I tion is to provide a simplified synchronizing pulse separator circuit.

Another object of this invention is to provide a separating circuit adapted to clip a portion of the amplitude of the synchronizing pulses-from a composite television signal.

Other and incidental objects and advantages will be apparent to those skilled in the art from a reading ofthe following specification andan inspection of the accompanying drawing i which Figure 1 is a block diagram of a television receiving system including a circuit showing one form of this invention,

Figures 2 and 3 are graphical illustrati-ons showing the operation of this invention, and

Figure 491s a circuit diagram showing another form of this invention.

Referring now in more detail to Fig. 1, a receiver and amplier such, for example, asthe type shown and described in Carlson Reissue Patent 20,700, patented April 19, 1938, is shown by block I having an antenna 3 and a ground 5. Signals from the receiver I are transmitted through one .channel to video amplifier 1 and thence to the control electrode 9 of the picture tube II through coupling condenser I3. The accumulated charge on the control electrode 9 is allowed to leak to ground through resistor I5. "Ihe picture tube II contains an electron gun including a cathode I6, the control electrode 9, a first anode I8 and -a second anode 20.

A portion of the composite television signal from the receiver and amplifier I is fed to the control electrode Il of the discharge device I9 which has a cathode 2 I, an anode 23 and a diodeanode 25 adjacent the cathode 2l. A cathode resisztlor 26 is provided in the circuit of the cathode A coupling condenser 21 and a grid leak resistor 29 are provided to maintain the control electrode Il at a proper bias potential with respect to ground. 'I'heanode 23 is supplied with its positive potential from a voltage source B+ across which is connected potentiometer 3l whose variable tap 33 is connected to the diode-anode 25 through resistance 35. I

The signal from the diode-anode 25 is then transmitted through a horizontal synchronizing pulsel channel and saw-tooth Wave generator represented by block 3l land thence to the horizontal deflecting coils 39 of the picture tube Il. The

. resented as the abscissa marked Es.'

plate current increases and likewise signal from the diode-anode 2s is a1so transmitted to the vertical synchronizing pulse channel and saw-tooth wave generator represented by block 4| and thence to the vertical deilecting coils 63 of the picture tube Il.

The operation of the separating circuit will now be explained. When a composite video signal from the receiver and amplifier is impressed upon the control electrode |1 oi' the triode section of the discharge device |9, the potential of sistor 26 causing the cathode 2| to change its po- Conversely,

when the control electrode I1 is made more negatential in the positive -direction.

tive, the conductance of the tube |9 is decreased so that very little current ows from cathode 2| y to anode 23; thus 'a smaller voltage drop exists across resistor 26 due to the reduced current so that the cathode 2| is less positive with respect to ground when the control electrode I1 is at a more negative potential. Y

` It will be Seen that if the potential on.v the diodefanode 25 is adjusted properly the signals passing through the discharge device |9 from the cathode 2| to the cathode-anode25 will be cut oil! beyond an amplitude where the potential ofthe cathode 2| exceeds in a positive' direction the potential on the diode-anode 25. In actual operation, the potential on'the diode-anode 25 will be adjusted so that it is equal to the potential of the cathode 2| when the potential on the con-l trol electrode |1 is at an amplitude greater than.

the blackest ofthe picture signals. Thus it will be seen that only the synchronizing pulses which. as before mentioned, are in the black" picture direction and of greater amplitude in that direction than the blackest picture signals, will be passed from the cathode 2| to the diode-anode 25 and thence to the synchronizing signal channels.

The circuit will also operate to stoppassing signals whose amplitudes arc above a predetermined level in a negative direction. For example, L

potential. When, control electrode i1 is more negative than' thecut of! value shown by point o of curve 45, no plate current. is drawn and the diode is positive' with respect to the cathode. so that a constant magnitude of diode current ilows as shown from c tod on curve l1. As electrode I1 becomes more positive (less negative) in accordance with the composite video and synchronizing signal impressed thereon, the cathode 2| increases in potential (becomes more positive) and the diode 'current decreases as shown from d to e of the curve 51. At some point, a, on curve 45 potential of diode plate 25 is controllable by slider 33 on voltage divider 3|.

Fig. 3 is another graphical illustration of the operation of this invention in which the composite signal 49 being fed to the control electrode I1 results in a clipping of the synchronizing pulses 5| to form a. diode current represented by curve 53. The diode current curve is illustrated by 55. Positive vpotential on the diode 25 is adjusted such Athat the potential o! the diode-anode 25 will equal that potential on the cathode 2|,when the.

such as indicated by' 51 will be eliminated so that the :top of the cl pped synchronizing pulsesl will be fiat such as in cated by curves 5I.

Fig. 4 illustrates another form of this invention I in which a potentiometer 59 is connected across if the signal on the control electrode |1 reaches a suilicient magnitude in a negative direction, the current flowing from the cathode 2| to the anode 23 will be cut oil at the cut-oil' point oi the tube I9. It is true that at this point there will be a' current owing from the cathode 2| to the anode 25 because the cathode 2| will be at substantially ground potential with respect to the diode-anode 25, but as the control electrode |1 goes farther negative than the cut-ofi' point there is no change in potential difference between the cathode 2| and the diode-anode 25 so that there will be no change in current flowing to the diode-anode'25 irrespective of change in the potential of the control electrode |1 beyond this cut-oil' point of discharge device I9.

The operation ci.' this separating circuit will be more fully understood by a reference to the graph illustrated in lfig. 2.

The voltage of the control electrode |1 is rep- Culve I represents the plate current i oi' the triade, and curve 51, the diode current is. The .magnitude is Y shown on the current axis oi' ordinates. It will` be seen that as the potential on control electrode |1 increases in the positive .direction the triade the .cathode a potential source 6| to furnish through variable tap 53 a bias potential for the control electrode |1 of the discharge device I9. This provides a means of adjusting the bias potential on the control electrode |1 such that the range 0f potentialsl at whichthe clipping circuit operates may be easily adjusted. By adjusting the potentiometer tap Il and the potentiometer tap B5 both limitations of the amplitude of the signal passed by the separating tube i9 may be readily ad- .lusted. A

While several systems for carrying this invention into effect have lbeen indicated and described,

it will be apparent to one skilled in the art that this invention is by no means to be limited by the particular organization shown and described but that many modiications thereof will be made Y without departing from the scope of this invention as set forth in theI appended claims.A

I claim as my invention: 1 e 1. In a television system ofythe type wherein synchronizing pulses are combined with picture signals, the combination of a discharge device having a cathode, an anode, and a control elec- V trode, means for impressing saldcox'nbined synchronizing'pulses and picture signals on said control electrode and adapted to cause said cathode to change its potential in accordance with said synchronizing pulses and `said picture signais, meansresponsive to changes in potential e.

of said cathode caused by said synchronizing pulses, means connected to said control elec-l trede to block said discharge device within the range of said synchronizing pulses.

2. In a television system of the type wherein synchronizing pulses are combined with picture signals, the combination of a discharge device 'ode to change its potential in accordance with i saidA synchronizing pulses and saidv picture signais, means responsive to a predetermined portion of changes in potential of said cathode, and means for blocking the current ow between said cathode and anode within the amplitude range of said synchronizing pulses 3. In a television system of the type wherein synchronizing pulses are combined with picture signals, the combination of a discharge device having a cathode, an anode, a diode anode adjacent said cathode, and a control electrode, means for impressing saidl combined synchronizing pulses and picture signals on said control electrode and adapted to cause said cathode to change its potential in accordance Withfsaid synchronizing pulses and said picture signals, means adapted 'to Supply a positive potential to said diode vanode to cause it to be responsive to changes in the potential oi' said cathode caused by said synchronizing pulses, and means for applying a bias to said control electrode to limit the response of said cathode to a portion of said synchronizing pulses.

4. In -a television system of the type wherein synchronizing lpulses are combined with picture signals, the combination of a discharge device having a cathode, an anode, and a control electrode, means for impressing said combined synchronizing pulses and :picture signals on said control electrode, a biasing potential applied to said control electrode to block the flow of current between said cathode and said anode during the greater portion of said synchronizing pulses, an impedance connected to said cathode adapted to cause said cathode to change its ,potential in accordance with said synchronizing pulses and said picture signals, and means responsive to changes in the potential of said cathode caused by said synchronizing pulses. DUDLEY E. FOSTER. 

